Firebird 2.1 Language Reference Update

Notes:
DML statements
select dbinfo.descr,
dbinfo.def_charset
from (select * from rdb$database) dbinfo
(descr, rel_id, sec_class, def_charset)
• Derived tables can be nested.
• Derived tables can be unions and can be used in unions. They can contain aggregate functions, subselects and
joins, and can themselves be used in aggregate functions, subselects and joins. They can also be or contain
queries on selectable stored procedures. They can have WHERE, ORDER BY and GROUP BY clauses, FIRST,
SKIP or ROWS directives, etc. etc.
• Every column in a derived table must have a name. If it doesn't have one by nature (e.g. because it's a constant)
it must either be given an alias in the usual way, or a column aliases list must be added to the derived table
specification.
• The column aliases list is optional, but if it is used it must be complete. That is: it must contain an alias for
every column in the derived table.
• The optimizer can handle a derived table very efficiently. However, if the derived table is involved in an
inner join and contains a subquery, then no join order can be made.
FIRST and SKIP
Available in: DSQL, PSQL
Added in: 1.0
Changed in: 1.5
Better alternative: ROWS
Description: FIRST limits the output of a query to the first so-many rows. SKIP will suppress the given number
of rows before starting to return output.
Syntax:
Tip
In Firebird 2.0 and up, use the SQL-compliant ROWS syntax instead.
SELECT [FIRST ()] [SKIP ()] FROM ...
::= Any expression evaluating to an integer.
::= The usual output column specifications.
Note
If is an integer literal or a query parameter, the “()” may be omitted. Subselects on
the other hand require an extra pair of parentheses.
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